Missing domesticated plant forms: can artificial selection fill the gap?

Abstract

In the course of their evolution, the angiosperms have radiated into most known plant forms and life histories. Their adaptation to a recently created habitat, the crop field, produced a novel form: the plant that allocates an unprecedented 30–60% of its net productivity to sexual structures. Long-lived trees, shrubs and vines of this form evolved, as did annual herbs. Perennial herb forms with increased allocation to asexual reproduction evolved, but there are no examples of perennial herbs with high sexual effort. We suggest that sowing seed into annually tilled fields favored shorter-lived herbs because of trade-offs between first-year seed production and relative growth rate and/or persistence. By propagating cuttings, people quickly domesticated tuber crops and large woody plants. Perennial herbs were too small to be efficiently propagated by cuttings, and the association between longevity, allogamy and genetic load made rapid domestication by sexual cycles unlikely. Perennial grain crops do not exist because they could not have evolved under the original set of conditions; however, they can be deliberately developed today through artificial phenotypic and genotypic selection.

Targeting perennial vegetation in agricultural landscapes for enhancing ecosystem services

“…Cox et al 275 argued, however, that perennial grain crops do have the potential to produce high and acceptable seed yields because (1) compared with annual crops, perennials tend to have longer growing seasons, greater canopy cover duration, and deeper rooting depths, allowing them to intercept, retain and utilize more precipitation, nutrients and light; and (2) perennials generally produce more above-ground biomass than do annuals and a greater proportion of that biomass might be reallocated to grain production through breeding. DeHaan et al 276 and Van Tassel et al 277 noted that low yields from perennial grain crops to date reflect a lack of attention from plant breeders and they predicted that artificial selection in a properly managed agricultural environment could increase seed yield while maintaining perenniality. In one of the few studies reporting the seed yields of perennial grain crops subjected to artificial selection, Scheinost et al 278 observed that promising lines of perennial wheat produced 1.7-5.8 Mg ha − 1 , as compared with 9.0 Mg ha − 1 from an annual wheat cultivar commonly grown in the area.…”

Strategies, Advances, and Challenges in Breeding Perennial Grain Crops

“…Virtually all of the annual grains that humans currently consume were developed through domestication. In brief, Neolithic peoples identified desirable wild plant species and subjected them to cycles of selection that favored "domestication" traits such as non-shattering (retaining seeds in seed heads until harvest), or uniform maturation of seed both on individual plants and across plant populations [9]. Once domestication traits were well established or "fixed" in populations, farmers were able to practice phenotypic selection to improve on seed yield and other desirable crop traits.…”

“…Other papers have addressed questions of why humans originally domesticated annual grain crops and what strategies make sense for domesticating new perennial grain crop species [8][9][10][11]. Relatively few papers, however, have been published that provide current overviews of progress in breeding specific perennial crops.…”

What Agriculture Can Learn from Native Ecosystems in Building Soil Organic Matter: A Review

“…Improvements in carbon balance, nutrient retention, soil water uptake efficiency, soil microbiome functions, and weed suppression are predicted as agriculture based on high soil disturbance is replaced by ecosystems that require minimal disturbance [36,82]. The reasons why early agriculturalists originally domesticated annual grain crops reflect the tools, energetic constraints and understanding of biological processes that humans had in the Neolithic era, 5000-10,000 years BP [83]. In the last century, the sciences of evolutionary biology, genetics and plant breeding have expanded tremendously, and many researchers believe it is now possible to breed perennial cereal, legume, fiber and oilseed crops that would yield sufficiently to eventually occupy large areas currently planted to annual species [80,84,85].When considering steps towards greater agricultural sustainability, the prospect of increasing ecological function through perennial crops is very significant, but so are discussions of land tenure, scale of production, energy return on investment and diversity of crops at both farm and regional scales [86][87][88].…”